1. Field of the Invention
The present invention relates to a tuner unit for suitable use in a television.
2. Description of the Related Art
FIG. 3 is a perspective view showing the principal part of a known type of tuner unit whose cover is partially cut out, and FIG. 4 is a cross-sectional view of the principal part of the tuner unit.
The configuration of the tuner unit will be described below with reference to FIGS. 3 and 4. A box-shaped frame 51 includes four metal side walls 52, and upper and lower openings 51a and 51b. 
A plurality of metal shielding plates 53 are provided in the frame 51 so as to partition the interior of the frame 51 into a plurality of compartments 54. An input coaxial connector 55 and an output coaxial connector 56 are attached to one of the side walls 52 so that they are spaced from each other.
Chip components 58, such as resistors and capacitors, are mounted on a wiring pattern (not shown) formed on the lower surface of a circuit board 57, and electrical components 59, such as coils, are mounted on the upper surface thereof while they are connected to the wiring pattern.
The circuit board 57 is also provided with a plurality of circuit blocks 60, such as an input distribution circuit 60a, an antenna tuning circuit 60, an RF tuning circuit 60c, a modulator circuit 60d, and an RF output circuit 60e. 
The circuit board 57 is placed inside the frame 51 in a state in which a terminal 57a protrudes outward from the frame 51.
When the circuit board 57 is placed in the frame 51, the shielding plates 53 standing upright on the circuit board 57 are positioned between the circuit blocks 60 including the input distribution circuit 60a and the antenna tuning circuit 60b. Thereby, the electrical components 59 are shielded from one another, and the circuit blocks 60 are electrically shielded from one another.
First and second covers 61 and 62 made of a metal plate include rectangular flat portions 61a and 62a, and retaining portions 61b and 62b bent from four edges of the flat portions 61a and 62a, respectively.
The first cover 61 is mounted so that the flat portion 61a covers the opening 51a and the retaining portions 61b retain the side walls 52. The second cover 62 is mounted so that the flat portion 62a covers the opening 51b and the retaining portions 62b retain the side walls 52.
Consequently, the interior of the frame 51 is shielded by the first and second covers 61 and 62.
In the above-described known tuner unit, since the input distribution circuit 60a and the antenna tuning circuit 60b are separated by the shielding plate 53 standing upright on the circuit board 57, the electrical components 59 must be mounted at a distance from the shielding plate 53. Therefore, the circuit board 57 occupies a large area at that position, and the size thereof is increased.
Moreover, since a plurality of metal plates are used for the shielding plates 53, the assembly efficiency is decreased, and the cost is increased.